Caption: Fluorapatite crystal. Image 2 of 8. Coloured scanning electron micrograph (SEM) of a fluorapatite, or calcium fluoride phosphate, crystal. This crystal has been grown in the laboratory for research into the use of fluorapatite as an ingredient in toothpaste to treat sensitive teeth. The fluoroapatite transfers fluoride ions to tooth enamel, which is a composite of collagen and hydroxyapatite (calcium phosphate), repairing any damage. As the crystal grows it changes from an hexagonal form to a spherical form. For a sequence of images showing this, see A630/373 to A630/380. Magnification: x6410 when printed at 10 centimetres wide.